Editing Lock (water navigation) (section)

===Staircase locks {{Anchor|Staircase locks}}{{Anchor|Staircase lock}}===
[[File:Bingley Five Rise Locks 1.JPG|thumb|left|Staircase of five locks, dating from 1774, at [[Bingley Five Rise Locks|Bingley]], England<ref>{{Cite news |date=2024-03-21 |title=Bingley Five Rise Locks mark 250th anniversary |url=https://www.bbc.co.uk/news/uk-england-bradford-west-yorkshire-68617233 |access-date=2024-12-01 |work=BBC News |language=en-GB}}</ref>]] 
Where a very steep gradient has to be climbed, a lock staircase is used. There are two types of staircase, "real" and "apparent".{{fact|date=March 2022}}

A "real" staircase can be thought of as a "compressed" flight, where the intermediate pounds have disappeared, and the upper gate of one lock is also the lower gate of the one above it. However, it is incorrect to use the terms ''staircase'' and ''flight'' interchangeably: because of the absence of intermediate pounds, operating a staircase is very different from operating a flight. It can be more useful to think of a staircase as a single lock with intermediate levels (the top gate is a normal top gate, and the intermediate gates are all as tall as the bottom gate). As there is no intermediate pound, a chamber can only be filled by emptying the one above, or emptied by filling the one below: thus the whole staircase has to be full of water (except for the bottom chamber) before a boat starts to ascend, or empty (except for the top chamber) before a boat starts to descend.

In an "apparent" staircase the chambers still have common gates, but the water does not pass directly from one chamber to the next, going instead via side ponds. This means it is not necessary to ensure that the flight is full or empty before starting.

Examples of famous "real" staircases in England are [[Bingley Five Rise Locks|Bingley]] and [[Grindley Brook]]. Two-rise staircases are more common: [[Snakeholme Lock]] and [[Struncheon Hill Lock]] on the [[Driffield Navigation]] were converted to staircase locks after low water levels hindered navigation over the bottom cill at all but the higher [[tides]] – the new bottom chamber rises just far enough to get the boat over the original lock cill. In China, the recently completed [[Three Gorges Dam]] includes a double five-step staircase for large ships, and a ship lift for vessels of less than 3000 metric tons. Examples of "apparent" staircases are [[Foxton Locks]] and [[Watford Locks]] on the [[Grand Union Canal#The Leicester Line|Leicester Branch]] of the [[Grand Union Canal|Grand Union]].

[[File:Thorpe Top Treble instructions.jpg|thumb|upright|left|Instructions for descending the flight of three locks at Thorpe Top Treble on the [[Chesterfield Canal]]]]
Operation of a staircase is more involved than a flight. Inexperienced boaters may find operating staircase locks difficult. Key concerns are either sending down more water than the lower chambers can cope with (flooding the towpath, or sending a wave along the canal) or completely emptying an intermediate chamber (although this shows that a staircase lock can be used as an emergency dry dock). To avoid these mishaps, it is usual to have the whole staircase empty before starting to descend, or full before starting to ascend, apart from the initial chamber.

One difference in using a staircase of either type (compared with a single lock, or a flight) is the optimal sequence for letting boats through. In a single lock (or a flight with room for boats to pass) boats should ideally alternate in direction. In a staircase, however, it is quicker for a boat to follow a previous one going in the same direction. Partly for this reason staircase locks such as Grindley Brook, Foxton, Watford and Bratch are supervised by lockkeepers, at least during the main cruising season, in which keepers try to alternate as many boats up, followed by down as there are chambers in the flight.

As with a flight, it is possible on a broad canal for more than one boat to be in a staircase at the same time, but managing this without waste of water requires expertise. On English canals, a staircase of more than two chambers is usually staffed: the lockkeepers at Bingley (looking after both the "5-rise" and the "3-rise") ensure that there are no untoward events and that boats are moved through as speedily and efficiently as possible. Such expertise permits unusual feats, such as boats travelling in opposite directions can pass each other halfway up the staircase by moving sideways around each other; or at peak times, one can have all the chambers full simultaneously with boats travelling in the same direction.